Active discharge collector for minimizing positive and/or negative charges on moving material webs

ABSTRACT

The invention concerns an active discharge electrode ( 5 ) for minimizing positive and/or negative charges on moving material webs. The active discharge electrode ( 5 ) comprises a plurality of needle-shaped individual electrodes ( 8 ) which are disposed mutually parallel and can be connected to a high-voltage source, preferably a high-voltage transformer. The active discharge electrode ( 5 ) further comprises at least one earthing conductor ( 11 ) extending at right angles to and along the plurality of individual electrodes ( 8 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to and active discharge electrode.

2. Description of the Prior Art

Discharge electrodes are known as passive discharge electrodes in theform of grounded points or tongues in a plurality of embodiments. Inaddition, there are also so-called active discharge electrodes which canbe connected to a source of high-voltage alternating current. They serveto discharge or eliminate positive and/or negative charges on thesurface of preferably fast-moving material webs, like those used forexample in gravure printing.

Usually these known active discharge electrodes have at least severalrows of needle-shaped individual electrodes arranged parallel to oneanother, said electrodes being arranged parallel to one another within arow with a point at their free ends and can be connected to a source ofhigh voltage. At least one ground conductor is located along a row ofelectrodes and preferably parallel thereto.

A study of such known active discharge electrodes has revealed thattheir efficiency during discharge is relatively poor and leaves arelatively high residual charge on the material web, especially onfast-moving material webs traveling at more than 2 to 3 meters persecond. The same is true of plastics with closed surfaces, for examplepolymer films such as polycarbonate or polyester with a breakdownvoltage of more than 4000 volts and a surface resistance of more than10¹⁴ ohms and a specific volume resistance of 10¹⁴ ohms per cm.

SUMMARY OF THE INVENTION

The invention is an active discharge electrode which permits the highestpossible charge in fast-moving material webs and in the above plastics,in which a double charge layer can form.

This goal is achieved in a discharge electrode according to the preambleof the main claim according to the invention by its characterizingfeatures in a surprisingly simple fashion.

Remarkably, it has been found that when a plurality of rows ofneedle-shaped individual electrons run parallel to one another, theresult of the discharge is not improved but on the contrary is even madeworse. It has been found according the the invention that a single rowof individual electrodes produces the best results. In addition, it hasalso surprisingly been found that efficiency is even further improvedwhen the ground conductor is completely surrounded by an electricalinsulator. Even with fast-moving material webs with a speed on the orderof more than 10 meters per second, a maximum possible discharge can beachieved. In the electrode according to the invention, there is also theadvantage if the power fails that the row of individual electrodes actas passive discharge electrodes so that at least a minimum of functionalability is retained despite the power failure. This effect, againsurprisingly, does not occur when the connections between the groundconductor and the individual electrodes are switched, in other words theground conductor is connected to a source of high voltage alternatingcurrent and the needle-shaped individual electrodes are grounded.According to the invention, the individual electrodes are connected to avoltage form the high voltage alternating current source that issymmetrical with respect to ground.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In particular, when two ground conductors are provided that are parallelto one another and are located on both sides of the row of individualelectrodes, an increase in efficiency and hence improved discharge areobtained.

When in addition each individual electrode is connected through an ohmicresistance to the high voltage source, effective protection againstcontact is provided at the same time, which shows a schematic crosssection through an active discharge electrode according to theinvention.

The discharge electrode marked as a whole by 5 has a profile 6 that hasa fastening groove 7 on the back for fastening the electrode.

It is provided with a single row of needle-shaped individual electrodes8 arranged parallel to one another, whose free ends are located on theopposite side relative to fastening groove 7. The row of individualelectrodes lies in a plane 9 indicated schematically in the drawing. Inaddition, each individual electrode 8 can be connected by an ohmicresistance 10 to the high voltage source, not shown, which represents asource of alternating voltage.

In addition, in the embodiment shown here, two ground conductors 11 areprovided that are parallel to one another and located on both sides ofthe row of individual electrodes 8, the ground conductors being circularin cross section and made of wire for example. These two groundconductors run at right angles to the direction of each individualelectrode 8 and parallel to the plane 9 in which the individualelectrodes of a row are located. Each conductor is surrounded by anelectrical insulator 12.

What is claimed is:
 1. An active discharge electrode for minimizingpositive and/or negative charges on moving material webs, with aplurality of needle-shaped individual electrodes located parallel to oneanother, which can be connected to a high-voltage source and with atleast one ground conductor that runs at right angles to and along theplurality of individual electrodes comprising: a single row of theplurality of parallel individual electrodes; and the at least one groundconductor is completely surrounded by an electrical insulator and isembedded in an electrical insulator.
 2. An active discharge electrodefor minimizing positive and/or negative charges on moving material webs,with a plurality of needle-shaped individual electrodes located parallelto one another, which can be connected to a high-voltage source and withat least one ground conductor that runs at right angles to and along theplurality of individual electrodes comprising: a single row of theplurality of parallel individual electrodes; the at least one groundconductor is completely surrounded by an electrical insulator; and thesingle row of the plurality of individual electrodes lies in a plane. 3.An electrode according to claim 1, wherein: the single row of theplurality of individual electrodes lies in a plane.
 4. An activedischarge electrode for minimizing positive and/or negative charges onmoving material webs, with a plurality of needle-shaped individualelectrodes located parallel to one another, which can be connected to ahigh-voltage source and with at least one ground conductor that runs atright angles to and along the plurality of individual electrodescomprising: a single row of the plurality of parallel individualelectrodes; the at least one ground conductor is completely surroundedby an electrical insulator; and ground conductors are provided that areparallel to one another and located on both sides of the single row ofthe plurality of individual electrodes.
 5. An electrode according toclaim 1, wherein: ground conductors are provided that are parallel toone another and located on both sides of the single row of the pluralityof individual electrodes.
 6. An electrode according to claim 2, wherein:ground conductors are provided that are parallel to one another andlocated on both sides of the single row of the plurality of individualelectrodes.
 7. An active discharge electrode for minimizing positiveand/or negative charges on moving material webs, with a plurality ofneedle-shaped individual electrodes located parallel to one another,which can be connected to a high-voltage source and with at least oneground conductor that runs at right angles to and along the plurality ofindividual electrodes comprising: a single row of the plurality ofparallel individual electrodes; the at least one ground conductor iscompletely surrounded by an electrical insulator; and each groundconductor is circular in cross section.
 8. An electrode according toclaim 1, wherein: each ground conductor is circular in cross section. 9.An electrode according to claim 2, wherein: each ground conductor iscircular in cross section.
 10. An electrode according to claim 3,wherein: each ground conductor is circular in cross section.
 11. Anelectrode according to claim 7, wherein: the ground conductor is a wire.12. An electrode according to claim 8, wherein: the ground conductor isa wire.
 13. An electrode according to claim 9, wherein: the groundconductor is a wire.
 14. An electrode according to claim 10, wherein:the ground conductor is a wire.
 15. An active discharge electrode forminimizing positive and/or negative charges on moving material webs,with a plurality of needle-shaped individual electrodes located parallelto one another, which can be connected to a high-voltage source and withat least one ground conductor that runs at right angles to and along theplurality of individual electrodes comprising: a single row of theplurality of parallel individual electrodes; the at least one groundconductor is completely surrounded by an electrical insulator; and eachindividual electrode is connected to the high-voltage source byresistance.
 16. An electrode according to claim 15, wherein theresistance is 250 megohms.
 17. An active discharge electrode forminimizing positive and/or negative charges on moving material webs,with a plurality of needle-shaped individual electrodes located parallelto one another, which can be connected to a high-voltage source and withat least one ground conductor that runs at right angles to and along theplurality of individual electrodes comprising: a single row of theplurality of parallel individual electrodes; the at least one groundconductor is completely surrounded by an electrical insulator; and thespacing of tips of the individual electrodes is between 1 and 2 cm. 18.An electrode in accordance with claim 17, wherein: the spacing isapproximately 1.5 cm.
 19. An active discharge electrode for minimizingpositive and/or negative charges on moving material webs, with aplurality of needle-shaped individual electrodes located parallel to oneanother, which can be connected to a high-voltage source and with atleast one ground conductor that runs at right angles to and along theplurality of individual electrodes comprising: a single row of theplurality of parallel individual electrodes; the at least one groundconductor is completely surrounded by an electrical insulator; and theelectrodes are connected to a high-voltage alternating-current sourcethat is symmetrical relative to ground.
 20. An active dischargeelectrode for minimizing positive and/or negative charges on movingmaterial webs, with a plurality of needle-shaped individual electrodeslocated parallel to one another, which can be connected to ahigh-voltage source and with at least one ground conductor that runs atright angles to and along the plurality of individual electrodescomprising: a single row of the plurality of parallel individualelectrodes; and the at least one ground conductor is completelysurrounded by an electrical insulator and the ground conductor isembedded in an electrical insulator, each individual electrode isconnected to the high-voltage source by resistance and the electrodesare connected to a high-voltage alternating current source that issymmetrical relative to ground.